The subject invention relates to a fluid actuated chuck wherein the piston-cylinder drive assembly is rotationally independent of the chuck body such that the necessity of providing rotating or running seals is eliminated.
In the prior art, power chucks are utilized in machining operations wherein a workpiece must be securely gripped and rotated at high speed. In such machining operations, chucks are provided which are adapted to be rotated by a drive means such as a lathe, and include radially movable jaws for gripping and releasing a workpiece. The chuck bodies are generally cylindrical in configuration with the master jaws being disposed at one end thereof and being capable of movement between a radially inward closed position and a radially outward open position. In use, a workpiece is placed parallel to the longitudinal axis of the chuck body and the jaws are closed radially inwardly about the workpiece. The rotation of the chuck body and the workpiece enables the latter to be machined. When the machining operation is completed, the jaws are urged into a radially outward open position releasing the workpiece.
Many power chucks in the prior art includes some type of actuator means such as a ring, which surrounds the periphery of the chuck body, and includes a plurality of keys engaged with the master jaws. Preferably, each key is disposed at an angle relative to the longitudinal axis of the chuck body such that the axial displacement of the actuator ring is operative to effect a radial movement of the master jaws.
In order to provide automatic, high speed, accurate operation of the latter prior art chucks, a fluid actuated drive assembly is provided which is operative to effect the axial movement of the actuator ring. The fluid actuated assembly includes a cylinder and a reciprocating piston which is actuated by fluid pressure, and the assembly further includes a plurality of rotating or running seals, disposed between the piston and the cylinder. The rotating seals which are generally formed from Teflon or graphite, are necessary to prevent fluid leakage between the piston and the cylinder. However, due to frictional forces inherent with running seals the rotational speed of a prior art chuck is limited. Further, at high speeds, fluid pressure within the rotating chamber builds up due to centrifugal forces often resulting in leakage and loss of clamping force. Even at low speeds, leakage will result from normal wear of the seals.
Accordingly, it would be desirable to provide an improved fluid actuated chuck wherein the piston-cylinder assembly is rotationally isolated from the chuck body, such that the requirement of providing running seals is eliminated.
Other prior art chucks which include fluid actuated jaws are disclosed in U.S. Pat. No. 3,918,352 issued Nov. 11, 1975 to Reich et al., U.S. Pat. No. 3,992,019 issued Nov. 16, 1976 to Crawshay, U.S. Pat. No. 4,032,161 issued June 28, 1977 to Peden et al., U.S. Pat. No. 4,032,162 issued June 28, 1977 to Flinchbaugh, and British patent specification No. 1,403,417 to Fink. The above cited patents disclose various hydraulic and pneumatic chucks having complex actuating mechanisms. Other methods previously used in the prior art to effect the actuation of the master jaws include fluid locking devices wherein internal valves are used to trap fluids. In the latter prior art chucks, leakage frequently occurs during the working cycle of the chuck resulting in seal failure, over heating and loss of chuck jaw clamping force.
Accordingly, it is an object of the subject invention to provide a new and improved fluid actuated chuck which eliminates the necessity of providing relatively unreliable running seals.
It is a further object of the subject invention to provide a new and improved fluid actuated chuck wherein the entire piston-cylinder drive assembly is rotationally immobile relative to the chuck body.
It is still a further object of the subject invention to provide a new and improved fluid actuated chuck wherein a transfer means is provided for transmitting the force generated by the piston-cylinder drive assembly to the actuator means of the chuck body for effecting the radial movement of the master jaws.
It is still another object of the subject invention to provide a new and improved fluid actuated chuck which includes a radial thrust bearing which is operative to transmit the axially directed forces generated by the piston-cylinder drive assembly to the actuator means, while enabling the drive assembly to remain rotationally immobile relative to the chuck body.